In recent years, miniaturization for reduction in cost, increases in numbers of pixels, and high functionality have progressed for CMOS (Complementary Metal Oxide Semiconductor) image sensors mounted on electronic devices such as mobile phone devices, digital still cameras, and digital video cameras.
In general, incident light incident on a CMOS image sensor is subjected to photoelectric conversion by, for example, a PD (photodiode) which is a photoelectric conversion portion included in a pixel. Then, a charge generated by the PD is transmitted to an FD (Floating Diffusion) which is a floating diffusion region via a transfer transistor, and an amplification transistor outputs a pixel signal with a level according to the charge accumulated in the FD.
In the related art, in a CMOS image sensor, a rolling shutter scheme of sequentially transmitting a charge from a PD to an FD for each row of pixels and reading the charge of the FD has been adopted. In the rolling shutter scheme, distortion has occurred in an image in some cases since exposure timings of the pixels are different between an upper-side row and a lower-side row of a CMOS image sensor.
On the other hand, in a CMOS image sensor including a charge accumulation portion for each pixel, a global shutter scheme of sequentially transmitting and reading charges from the accumulation portions to FDs after simultaneously transmitting the charges from PDs to the charge accumulation portions for all of the pixels has been developed. In the global shutter scheme, distortion can be prevented from occurring in an image since exposure timings of all of the pixels are identical.
In a CMOS image sensor in which the global shutter scheme is adopted, an accumulation time of a charge in a charge accumulation portion or a diffusion layer formed in a pixel is longer than in the rolling shutter scheme. For this reason, spouting of electrons on the surface of a semiconductor substrate may increase in a diffusion layer (high-concentration N-type region) of the charge accumulation portion, and thus a dark current may increase.
Accordingly, the applicants of the present application have been developing a solid-state imaging element capable of suppressing occurrence of a dark current, for example, by applying a negative charge to an upper light-shielding film of a PD so that a hole is filled and by absorbing a dark current occurring in an interface in the hole.
Also, in a CMOS image sensor disclosed in Patent Literature 2, a diffusion layer portion (high-concentration N layer) is formed by a process of forming a capacitor film inside a pixel or a passage through which a charge accumulated in a capacitor inside the pixel is transmitted.